Britain must step up its construction of offshore wind farms if it is to meet its target of producing 15% of energy needs from renewable sources, the chief executive of a leading utility said yesterday.

At the present rate, Britain is on course to produce between 5% and 7% of its energy from renewables, Scottish and Southern Energy's Ian Marchant said.

"The solution is to explore offshore wind. To meet the target we are going to need 25 gigawatts of offshore wind power."

Industry experts calculate that, to meet the 15% target, Britain would need to generate around 35% to 40% of its electricity from renewables, with much of that coming from wind farms.

Last week, SSE signed a lease with the Crown Estate to build a £1.3bn wind farm at Greater Gabbard, 26 kilometres off the Suffolk coast, which will be the country's largest. It will have generating capacity of 504 megawatts - half the output of an average coal-fired station. Due to be operational by 2011, it will produce enough electricity to power 415,000 homes .

Marchant said the UK needed to build four wind farms a year the size of Greater Gabbard to meet the renewables target.

Yesterday, the Crown Estate announced the procedure for companies to apply for offshore wind farm development in Scotland. It is seeking applications for wind farms with at least 100 megawatts of capacity. Scotland's energy minister, Jim Mather, said: "We want to see more offshore turbines in appropriate locations around the Scottish coast."